Audio: Fix abnormal keytone playback during silent mode changing

Change-Id: Icfc4003c9756b3c33578c137e59dc4a2b4f25647
Author: Chenyang Du <chenyang.du@intel.com>
Signed-off-by: Ertao Zhao <ertaox.zhao@intel.com>
Signed-off-by: Shuo Gao <shuo.gao@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>
Signed-off-by: Jack Ren <jack.ren@intel.com>
Author-tracking-BZ: 19084 4898